Ballistic protection concerns protection against kinetic energy or pressure caused by projectiles such as bullets, gravity bombs, rockets etc. Ballistic armor works by decreasing the energy density of the projectiles, for example by affecting the shape or postion of the projectile, by breaking the projectile and/or by decelerating the velocity of the projectile. Ballistic armor against pressure caused by ammunition works by absorbing or directing the energy of the shock wave.
A ballistic armor may be produced of almost any material when the mass is sufficient enough. However, especially land, sea and air vehicles benefit when the armor is as light as possible, and further when the armor works as the load-bearing structure. Often there is also a requirement for the armor to fit into a small space, i.e. practically speaking the thickness of the structure needs to be as thin as possible.
Traditionally, metallic structures, for example High Hardness Steels have been used in the production of ballistic armors. However, the cores of some projectiles aimed for penetrating armors, i.e. the penetrator, have such a high hardness that the hardness of the metallic armor structures are insufficient to cause damage to these penetrators. Therefore, the armor structure in these cases works by absorbing the kinetic energy of the projectile. The armor structures intended against these penetrators become excessively massive as a monolithic metallic structure, especially when applied to vehicles.
As known from prior art, ceramic elements and metallic ceramic composites, such as aluminum oxide (Al2O3), silicon carbide (SiC), boron carbide (B4C), tungsten carbide (WC), boron nitride (BN), silicon nitride (Si3N4), carbon nitride (C3N4), titanium diboride (TiB2), may be used in ballistic armors. Such materials may have a hardness sufficient to generate damage to the projectiles. Ceramic materials are known to have high compressive strength, but at the same time weak tensile strength.
The simplest construction principle when using ceramic elements in a ballistic armor is gluing rectangular prism ceramic elements, such as bricks, to a frame structure, such as a fiber composite laminate. The manufacturing methods when using ceramics most often require piling the elements manually on a panel-shaped mold of the desired final product, i.e. because the aftertreatment (for example cutting into shape) of the ceramic elements is difficult due to their high hardness. Typical armors that have ceramics glued to a frame structure do not withstand bending load. Therefore, such armors do not work as load-bearing structures in vehicles, for example. Instead these armor structures form a structural parasitic weight (excessive weight).
According to prior art it is also known that ballistic armors may be improved by, either fully or partly, encapsulating ceramic elements. This is known to                i) delay the fracturing of the ceramic surface and the start of the penetration        ii) slow down the cracking of the ceramic element        iii) keeping the ceramic material in contact with the penetrator and thus increasing the erosion of the penetrator        iv) affecting the fracturing and shaping of the ceramic elements caused by a shock wave with the adaption of the ceramic elements and the encapsulating material's acoustic impedance.        
Prior art tells that the shock resistance of ceramic elements increases significantly when molten metal, such as aluminum, is casted on top of the ceramic elements. The big difference in the ceramic elements' and aluminium's thermal expansion creates a compressing pretension for the ceramic elements when the molten metal cools down to solid material contracting at the same time.
The manufacturing complexity is a common characteristic for the presented structures. The known structures are also limited to a predefined shape. It has been difficult to adapt existing solutions to serial production as well. Even though there is a clear benefit due to the fact that the ceramic elements get a pretension when compressed by a metal casing, one disadvantage is that the existing methods require high accuracy for dimensional tolerances.